Information processing apparatuses are equipped with various types of cooling mechanisms.
Some information processing apparatuses have redundancy. For example, high reliability and stable operation are expected from information processing apparatuses, such as a server and a communication apparatus, used in a large-scale core system. In some cases, meanwhile, space saving is expected from information processing apparatuses. In other cases, for example, lots of components have to be mounted at high density on a 19-inch rack defined by Electronic Industries Alliance (EIA) standards and other standards, when an information processing apparatus is designed which is fitted in the 19-inch rack.
The redundancy of an information processing apparatus is usually achieved by using multiple components that exerts the same function. In the case of a cooling system, for example, installation of two or more cooling fans for a single apparatus to be cooled makes the apparatus capable of continuing its operation even when one of the cooling fans goes out of order. The installation of two or more cooling fans for a single apparatus, however, increases the space occupied by the cooling fans. Although a conceivable option to achieve the redundancy while avoiding the space increase is to install multiple downsized cooling fans, the option is impracticable. That is because: when a cooling fan is downsized, a rate of a decrease in cooling performance of the cooling fan is larger than a rate of the reduction in the size of the cooling fan; and thus, the downsizing of the cooling fan remarkably decreases the cooling performance of the cooling fan. Accordingly, the redundancy achieved by downsizing the cooling fans likely makes it impossible to maintain the cooling performance demanded by the apparatus to be cooled.
The followings are reference documents.    [Document 1] Japanese Laid-open Patent Publication No. 2007-179655 and    [Document 2] Japanese Laid-open Patent Publication No. 61-194899.